​​​​العلاقة عمق الميدان والرقم البؤري للعدسة (f , No ) .. كتاب أسس التصوير الضوئي

Relationship depth of field and focal number of the lens (f , No )

From balancing between the two previous examples 2 and 3, we note that the result that we have reached supports what has been mentioned above regarding the effect of widening or narrowing the aperture of the diaphragm on the depth of field that you obtain. According to the previous solutions, we find the following:
With an aperture of 4 f, we obtained a depth of field in an area between 6.33 meters to 20 meters to infinity, meaning that the narrower the diaphragm aperture (with other factors remaining constant) the depth of field area.

The depth of field is thus inversely proportional to the diameter of the diaphragm aperture. The larger the diameter of the diaphragm aperture, the smaller the depth of field area.

Summary of the relationship between depth of field and the factors affecting it

We can summarize this relationship as follows
(1) The field is inversely proportional to the square of the degree of magnification of the image, as we noticed that as the image is enlarged, the diameter of the mixing circles increases, so the sharpness of the details in the image decreases (i.e. the depth of field decreases in other words). Assuming that the image is small or enlarged.


(2) The depth of field is inversely proportional to the square of the focal length of the lens, for all of them, the longer the focal length of the lens, the smaller the depth of field.
(3) The depth of field is directly proportional to the square between the object: it increases with the increase in the distance between the object and the lens.
(4) The depth of field is directly proportional to the focal number of the lens, so the higher the number (i.e. the narrower the diaphragm aperture), the greater the depth of field.